Fbiedbich lehneb



UNITED STATES PATENT OFFICE.

FRIEDRICH LEHNER, OF ZURICH, SlVl'lZERLAND.

ART OF PREPARING ARTlFlClAL. SlLK.

SPECIFICATION forming Application filed April 16, 1895.

To all whom it may concern.-

Be it known that I, FRIEDRICH LEHNER, a citizen of Germany, residing at Zurich, Switzerland, have invented certain new and useful Improvements in the Art of Preparing Artificial Silk; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will en able others skilled in the art to which it appert ains to make and use the same.

This invention relates to the art of producing, artificially, a fiber or thread having the glossy appearance and all the desirable characteristics and quality of natural silk and other threads produced by organic beings.

More particularly the invention relates to the art of producing such threads or fibers, which involves as an important step the nitration of cellulose.

The object of the said invention is to produce a thread possessing greater strength and stability of structure than those obtained under the processes heretofore practiced, and, with this object in view, my said invention involves the production or separation and fixing of nitrocelluloses differing, essentially, from those usually obtained in this and other arts.

Briefly stated, the essential features of my invention, which consists in the process .described and the product resulting therefrom, are as follows: The new process embodying my invention starts out with the production and isolation of trinitrocellulose and tetranitrocellulose instead of the mixture of di, penta, and hcxa nitrocellulose, which formerly was always obtained as the basis of the process. The tri and tetra nitrocellulose are always obtained together and have not been separated from each other. The new process, moreover, involves the fixing for the desired time of these two nitrocelluloses, which heretofore, even when produced, were rapidly converted into the other nitrocelluloses. This fixing is performed by the agency of free sulfuric acid. In order to produce a perfectly homogeneous mixture of nitrocelluloses, I have found that it is necessary to gradually add the cellulose to the nitratingbath and to gradually raise the temperature of the nitrating-bath as the nitration proceeds.

After the completion of the nitratin g part of Letters Patent No. 562,626, dated June 23, 1896.

erial No. 545,931. (No specimens.)

process the product, consisting mostly or entirely of tri and tetra nitrocellulose, in a homogeneous mixture, is freed, as far as possible, from the nitrating-acids by centrifugal action, and not by washing in water and drying, the method heretofore adopted, and which always resulted in a slow transformation of a portion of the nitrocellulose. It is then immersed into sulfuric acid and again subjected to centrifugal action, and the acid-wet resultantmass is then mixed with a vulcanized drying-oil for the purpose of maintaining the otherwise unstable nitro compounds unchanged, and later, after the nitro groups have been deoxidized, to fill the pores of the fiber with cement-like filling. The mixture thus produced is then dissolved in a suitable solvent and drawn into a thread. The thread so produced is then submitted to a deoxidation of the nitro groups to render the same less easily combustible and susceptible of bein g dyed by the usual method. By this means an intermediate compound is produced which, though not a nitrocellulose or amido compound, is not cellulose, but a peculiar new compound, consisting of cellulose combined with nitrogen and insoluble in the solvents of nitrocellulose.

Having thus outlined the process forming part of myinvention, Iwill now more particularly describe the same.

C-ellulose in any form such as wood, cotton, jute, ramie, and the like, and, when necessary, reduced to filaments and freed from mechanical and chemical impurity, is dried and nitrated in the following manner: The well-dried cellulose is, in small quantities, gradually introduced into a mixture of three volumes sulfuric acid of 66 Baum and two volumes of nitric acid from 131 to 1.32 specific gravity, at an initial temperature of 30 Celsius. At each fresh addition of cellulose care is taken that the nitrating-acids are at a somewhat higher temperature. The temperature is then increased progressively up to,but not exceeding, 40 Celsius. Finally, the whole mixture is maintained at this temperature for several hours. Under this process, principally tri and tetra nitrocellulose are obtained, other nitrocelluloses being present only in small quantities. They are freed as much as posoccurring in nature,

sible from the adhering nitrating-acids by centrifugal action in a manner su-fiiciently ble to dye it by the usual methods in this condition. It is, therefore, submitted to dewell understood by those skilled in the art, oxidation. This deoxidation mi ht, as 1s and hence needing no further explanation known, be effected by partially eliminating The weight of the nitrocellulose produced is the nitro groups in the nitrocellulose by heatrednced to about forty per cent. by this treating the same with sulfur compounds, which ment. The nitiating-acids are recovered give off sulfureted hydrogen. This method, and may be used for fresh nitration by however, is objectionable, for the reason that strengthening them by the addition of strong it seriously impairs the firmness of the nitric acid. The nitrocellulose, damp with threads. The product always snfiers and acid, is then placed into sulfuric acid of may, in fact, be rendered quite worthless about 1 35 specific gravity It is well disthereby. Moreover, I have found that an t11bnted therein and again submitted to cenalkaline deoxidizing agent reacts quickl 8o trifugal action, after which amass remains, but greatly prejudices the firmness of the containing said nitrocellulose with about thread. I have also found that the firmness forty per cent. of sulfuric acid of 1.4 speof the thread after deoxidation greatly decific gravity and. some nitric acid. The prodpends upon uniformityof the product worked uct, damp with sulfuric acid, is now mixed upon with regard to its degreeofnitration. witha vulcanized drying-oil, which may be By the process so far described, I obtain a obtained by treating. any oil which dries in product having such a high uniformity of the atmosphere, such as, e. 9., cotton-seed oil, nitration.

poppy-oil, linseed-oil, nut-oil, &c.,.in the fol I prepare a deoxidiziug liquid which will lowing. manner: The oil to be treated is dinot injure the thread and which avoids injuo luted with half its weight of sulfuric ether rious alkalinity, in the following manner:

in order to prevent too quick a reaction. To Concentrated ammonium hydiosulfid 1ethis from ten to twenty per cent. of sulfur pared in any of the usual ways is diluted chlorid (according to'the nature of the oil and with water to about ten per cent and in it a the consistency of the liquid required) is suitable-neutral magnesium salt is dissolved 5 slowly added while continually shaking the in aboutequivalentpropoitions Thethieads mixture. After a short time it is found that are dipped lnto this liquid at about 40 Cela reaction has taken place and a yellow prod slus, and kept them until the ialnbow colors net 01 precipitate has sepaiaied out The of cellulose are visible under the microscope latter quickly settles and the thick clear liq in polarized light The thread is thereupon roo uid is separated therefrom by decanting. washed in much water, dried, and finished. About ten percent. by weight of the vulcan- In lieu of the ammonium hydrosulfid, poized oil or chemically-transformed liquid so tassium or sodium hydrosulfid may be used obtained is then added to the acid-w et nitro together with amagnesium salt. In order to cellulose last obtained, and the whole mivprevent the precipitation of magnesia, any ture then dissolved inabout five times its suitable ammonium salt is added, wherebya weight of' methyl alcohol acetone or ethylsolubleammonium-magnesium-saltisformed. alcohol alcohol-ether. After filtration it Although I speak. in the above of a deoxiforms-the rawmaterialorsolution from which dation of the nitrocellulose and a retrogresthe artificial thread or fibe1 is produced sion of the same into, or, rather, toward pule no lhis artificial thread is formed by simply alcellulose, by reduction with sulfureted hylowing the solution to flow out from an or1- drogen, which is the generall -accepted exfice, pieferably from one-fourth to one-half planation of the reaction, I have always mllliineter in diameter, into a suitable llquld found that the resultant compound thou h or congeal'ing bath or dii ectlylnto the atmosa derivative of cellulose, always contains n1- II 5 phere. lhe threads are by this means 111- trogen Inasmuch as the same contains n1- stantly solidified and aremore 01 less fine actrogen, it is not cellulose. On the other hand, cording to the leater orlesser speed at wh1ch it is insoluble in the solvents of nitrocellut ey are drawn out. They are immediately lose, and has other properties which distintwisted or spun on the same machine. The guish it from the same. It, therefore, is not twisted threads wound on suitable spools or nitrocellulose, or an amido compound, but otherwise aiewaunedfora1on time in water rather a peculiar substance of its own kind,

as soon as possible whereby the g1 eater part of which is an intermediate compound between the fi ee acid in the thread is removed the1e the same and cellulose.

from The solvent methyl-alcohol acetone The advantages and novel results flowing I2 5 ethyl-alcohol, ether, or the like is also driven from my invention may, perhaps, be best out and may be partially recovered. By this shown by comparing the same with the art as treatment with warm water the combinaheretofore practiced.

tion of the nitrocellulose with the vulcanized Nitration has hitherto been effected b y imoil, mechanically and chemically, is strongly mersing the cellulose for a long time into a 1 0 mixture of sulfuric and nitric acids, or saltpeter, then squeezing out the nitrating-acids, thoroughly washing the nitrocellulose or yroxyline several times in water, until there is no longer any acid reaction, and then drying at a low temperature and dissolving in a suit able solvent. By this process several different nitrated products of cellulose are obtained, ranging from dinitrocellulose to hexanitrocellulose, and this mixture is what is commonly known under the name of pyroxylin. Naturally, the port-i on of the cellulose first bro ught into contact with the nitrating-acids becomes most highly nitrated, the acids being then more concentrated. As the nitration proceeds, the acids become gradually weaker and hence lower nitrates are produced. Moreover, my experiments have shown that the after treatment of the nitrocellulose and the washing with water after removal of the nitrating-acids gives rise to a slow transforma tion, particularly of the tri and tetra nitrocellulose, and this transformation is hastened by the drying process.

The nitrocelluloses formed are the following: dinitrocellulose, G, I, (NO )2O trinitrocellulose, G l-I,;(NO )3O tetranitrocellulose, O H lN O )4O pentanitrocellulose, G, lI, (N() )5O hexanitrocellulose, E, (N O )6O,. Of these, the dinitrocellulose, pentanitrocellulose, and hexanitrocellulose are the constant products, and, when obtained in the usual way, are always mixed. They are, however,not very suitable on account of their low degree of solubility in the usual solvents. Moreover, the very great difference in the degree of nitration of these components causes a great inequality in the subsequent retrogression toward cellulose in the process of deoxidation. This inequality is very disadvantageous with regard to the strength of the thread produced.

Host thorough investigations and experiments conducted by me, moreover, have shown that the trinitrocellulose and the tetranitrocellulose are the most suitable compounds for producing a thread of the requisite strength, on account of their high degree of solubility in the ordinary known solvents of pyroxylin. Their solution, in a high degree of concentration, in such solvents is not of a glue-like consistency, as is the case with the other nitrocelluloses, and it may be readily worked, and subsequently it can be well deoxidized. The tetranitrocellulose and trinitrocellulosc when obtained free from or mixed only with a small amount of the other nitrocelluloses have the advantage of differin g only a little in their degree of nitration, and, hence, their subsequent retrogression toward cellulose is very uniform. They, therefore, yield a thread of much greater strength and tenacity than when the other nitrocelluloses are employed.

The tri and tetra nitrocellulose are ordinarily obtained together with other nitrocelluloses, but heretofore, as before stated, they are, by the further treatment of pyroxylin, converted into the lower dinitrocellulose and the higher penta and hose nitrocellulose.

The presence of free sulfuric acid, upon which one feature of my invention is based, and the omission of the washing anddrying step, however, eifectually prevent or greatly retard this conversion. This I have demonstrated in the following way: Optically, in polarized light, dinitrocellulose appears uniformly clear, either directly after nitration or when precipitated from a collodion solution. It is only distinguished from cellulose in that the colors of the spectrum do not appear. This is the case, even if the material be washed for a long time with water and then dried. Pentanitrocellulose appears brown, with dark-blue stripes. It can be made by dissolving nitrocellulose in nitric acid and precipitating with sulfuric acid. I-Iexanitrocellulose appears in pure blue lines. Trinitrocellulose combined with tetranitrocellulose (they cannot be obtained separately or isolated) after nitration, and when the acids have been pressed out, appear, without any further treatment, glossy and of a feeble yellow color, without colored stripes or lines. If, however, they are freed from the acid by washing and gently warmed, the dark-brown stripes of the pentanitrocellulose appear directly in polarized light, indicating that the conversion into the higher nitrocellulose has taken place.

My treatment of the product with sulfuric acid after nitration, and the omission of the washing and drying steps in the process, hence favors the persistence of the uniform nitration and the yield of only the tri and tetra nitrocellulose. No appreciable heating of the fiber takes place, and decomposition does not set in, as is always the case on immersion into water. Above all, no higher product of nitration is formed. The nitrating-acid is also removed partly by the sulfuric acid and partly mechanically, so that the washing with water and subsequent drying, which I have shown to be incompatible with the production of the tri and tetra nitrocelluloses, for the purpose of removing the nitrating-acids, is avoided.

The advantage of that feature of my invention which consists in gradually adding the cellulose to the nitrating-bath and progressively raising the temperature of the bath after each fresh addition of cellulose is that a uni-.

form product of nitration is obtained and not, as heretofore, a product varying greatly in the degree of nitration of its constituents, which, as above stated, seriously afiects the strength of the thread produced, in view of the unequal retrogression of these products toward cellulose.

Under the old methods, where the cellulose was all introduced into the nitrating-bath at one time and the bath was maintained at the same temperature throughout the entire process, the portion of the cellulose first acted upon by the nitrating-acids yielded the higher products of nitration and, as the bath became Weaker, lower products of nitration were produced. A Very unequal pyroxyline or nitro product was hence formed. This very undesirable result is obviated by the new treatment invented by me, and which, as stated, involves the gradual introduction of the cellulose into the nitrating-bath and the progressive heating of the same as the addition of fresh cellulose proceeds.

The advantage of the addition of the chemically-altered drying-oil is that thereby the otherwise unstable nitro compounds (the tri and tetra nitrocellulose) are maintained unaltered and uniformly nitrated'. Another advantage is that thereby an unalterable compound is introduced and later on after deoxidation remains present between the moleculesof the thread or fiber, thereby filling the same as with a cement and obviating too great looseness in its texture. This closing upor cementing of the'fiber is hastened by the small quantity of nitric acid from the nitrat-' 2. The process which consists in-gradually introducingcellulose into a mixture ofsulfuric and nitric acids, in the proportions and densities, substantially as specified, and raising the temperature of the mixture at each fresh addition of cellulose.

3. The process which consists in gradually introducing cellulose into a mixture of sulfuric and nitric acids, in the proportionsand densities substantially as specified, and raising the temperature of the mixture at each fresh addition of cellulose, and finally maintaining the whole mixture at the final temperature for several hours.

4. The process'which consists in gradually introducing cellulose into a nitrating-bath, and-progressively raising the temperature of the nitrating-bath as the introduction of the cellulose proceeds, and treating the nitrocelluloscs thus produced with sulfuric acid, to remove the nitrating-acids andto prevent the conversion of the nitrocelluloscs obtained.

5. The process which consists in gradually introducing cellulose into a nitrating-bath, and progressively raising the temperature of the nitrating-bath as the introduction of the cellulose proceeds, and treating the nitrocelluloscs thus produced with sulfuric acid, to remove the nitrating-acids and to prevent the conversion of the nitrocelluloscs obtained,and mixing the acid-wet nitrocellulose with vulcanized oil.

6. The process which consists in gradually introducing cellulose into a nitrating-bath,

and progressively raising the temperature of the nitrating-bath as the introduction of the cellulose proceeds,treating the nitrocelluloscs thus produced with-sulfuric acid, to remove the nitrating-acids and to prevent the conversion of the nitrocelluloscs obtained, mixing the acid-wet nitrocellulose with vulcanized oil, and dissolving the mixture in acetone, an

alcohol or alcohol ether.

7. The process which comprises the followin g steps: gradually introducing cellulose into a nitrating-bath and progressively raising the temperature of the bath as the cellulose is added, then maintaining the whole mixture at the final temperature for several hours, then separating the nitrating liquid by centrifugal action, then immersing the acidmoist resultant mass in sulfuric acid, then adding thereto a vulcanized drying-oil, and finally dissolving the mixture in asuitable solvent, such as acetone, an alcohol or alcohol ether, all substantially in the manner and in the proportions set forth.

8." Theprocess which consists in drawing a thread froma mixture of trinitrocellulose and tetranitrocellulose with a vulcanized drying,

oildissolved in a suitable solvent, then immersing the same for a long time in warm water, and finally dipping the threads in'a solution of thehydrosulfid of an alkali metal or radical and a neutral magnesium salt, to reduce the combustibility of the thread.

9. The'process which comprises the following steps gradually introducing cellulose into a nitrating-bath and progressively raising the temperature of the bath as the cellulose is added, then maintaining the whole mixture at the final temperature for several hours, then separating the nitratin g'li quid by centrifugal action, then immersing the acid-moist resultant mass in sulfuric'acid, then adding thereto avulcanized drying-oil, then dissolving the mixture in asuitable solvent, and finally immersing the same in a solution of the hydrosulfid of an alkali metal or radical, to reduce the combustibility of the thread.

10. The process which consists in dipping a thread consisting substantially of dinitrocellulose and tetranitrocellulose into a solution containing about ten per cent. of ammonium or other alkali hydrosulfid and a neutral magnesium salt at about 40, Celsius, and keeping the same therein until the rainbow colors of cellulose are visible under the microscope in polarized light.

11. The process which comprises the following steps: gradually introducing cellulose into a nitrating-bath and progressively raising the temperature of the bath as the cellulose is added, then maintaining the whole mixture at the final temperature for several hours, then separating the nitrating liquid by centrifugal action, then immersing the acid-moist resultant mass in sulfuric acid, then adding thereto a vulcanized drying-oil, and finally dissolving the mixture in a suit- IIO able solvent, such as acetone, an alcohol or alcohol ether, then drawing the thread and immersing the same in Warm water, and finally dipping the same in a solution to reduce the combustibility of thesame.

12. The process which comprises the following steps: gradually introducing cellulose into a nitrating-hath and progressively raising the temperature of the bath as the cellulose is added, then maintaining the Whole mixture at the final temperature for several hours, then separating the nitrating liquid by centrifugal action, then immersing the acid-moist resultant mass in sulfuric acid, then adding thereto a vulcanized drying-oil, and finally dissolving the mixture in a suitable solvent, such as acetone, an alcohol or alcohol ether, then drawing the thread and immersing the same in Warm Water, and finally dipping it into a solution of ammonium or other alkali hydrosulfid and a neutral magnesium salt at about 40, Celsius.

13. The process which comprises the followkali hydrosulfid, and finally Washing, drying and finishing the same.

In testimony whereof I afiix my signature in presence of two Witnesses.

FRIEDRICH LEHNER. Witnesses H. HALBERG, EMILIE MAJORES. 

